org-agenda-columns-compute-summary-properties

org-agenda-columns-compute-summary-properties is a variable defined in `org-agenda.el'.
Its value is

t

Documentation:
Non-nil means recompute all summary properties before column view.
When column view in the agenda is listing properties that have a summary
operator, it can go to all relevant buffers and recompute the summaries
there. This can mean overhead for the agenda column view, but is necessary
to have thing up to date.
As a special case, a CLOCKSUM property also makes sure that the clock
computations are current.

You can customize this variable.